1. Field of the Invention
The present invention relates to a process for treating heavy hydrocarbons by ultrafiltration. Heavy hydrocarbon feed containing detrimental quantities of metals and/or Conradson Carbon Residue (CCR) and/or asphaltenes is fed to a first ultrafiltration stage wherein it is contacted with a first ultrafiltration membrane to produce a first permeate and a first retentate. The first permeate is sent as feed to a second ultrafiltration stage wherein it is contacted with a second ultrafiltration membrane which is identical to the first ultrafiltration membrane, thereby producing a second permeate and a second retentate. The second permeate unexpectedly has a lower level of metals and CCR than does the first permeate. The second permeate, if of low enough metals and/or CCR and/or asphaltenes content can be used as cat cracker feed, or it can be sent as feed to a third ultrafiltration stage for contacting with a third ultrafiltration membrane, again identical to the first ultrafiltration membrane. The retentates from each zone can be combined, or the retentate from downstream stages can be recycled to the previous upstream stage for combination and coprocessing with the feed to that previous stage.
Stated differently, the process involves multiple ultrafiltration stages, each stage using the same membrane material, wherein the permeate from the previous upstage stage is used as feed to the next lower downstream stage, any number of such stages being used in series until permeate of the desired quality is obtained.
2. Description of the Related Art
The treatment of heavy hydrocarbon feed by ultrafiltration is known in the art.
U.S. Pat. No. 4,411,790 teaches the ultrafiltration of hydrocarbon feeds by circulating the feed through at least one module having an inorganic barrier coated with a metal oxide layer. The process can be used to regenerate used lube oils or for reducing the asphaltene content of heavy oils (e.g., vacuum residue). The barrier is preferably a porous metal or ceramic support with a pore radius of 50 to 250 .ANG.. The metal oxide layer can comprise TiO.sub.2, MgO, Al.sub.2 O.sub.3, SiO.sub.2 or an Al.sub.2 O.sub.3 based mixed oxide (e.g., Al.sub.2 O.sub.3 -MgO; Al.sub.2 O.sub.3 -SiO.sub.2).
Multiple elements can be used in series with the permeate from one element being used as the feed to a subsequent downstream unit. The different modules may contain barriers having different pore radii e.g., the first barrier of radii 200 .ANG., the following of 150 .ANG. and so on.
U.S. Pat. No. 4,814,088 is directed to a process for removing high molecular weight components and inorganic compounds from oil feeds by passing the feed across the high pressure side of a microporous membrane so that oil depleted in the high molecular weight and inorganic component permeates through the membrane leaving a retentate rich in high molecular weight components and inorganic compounds. Preferred membranes are polysulfones, polyacrylonitriles, polyamides and polyvinylidine fluorides. Molecular cut off is preferably less than about 10,000 in aqueous medium and less than 4000 in oil.
U.S. Pat. No. 4,816,140 is directed to a process for deasphalting a hydrocarbon oil using a hydrocarbon solvent containing 3 to 8 carbons. The solvent is recovered from the deasphalted oil by passing the solvent/oil solution across an inorganic membrane of pore radii from 2 to 15 nonometers to recover solvent as permeate and oil as retentate.
U.S. Pat. No. 4,750,990 is directed to a process for the membrane separation of hydrocarbons using cycloparaffinic solvents. A heavy crude oil containing metals may be separated from light hydrocarbon oil by passing a solution of the crude oil dissolved in a C.sub.5 to C.sub.8 cycloparaffin through a polymeric membrane. The light oil will be recovered as permeate and a heavy oil containing the metal contaminants will be recovered as retentate. The membrane possesses pore sizes in the range of from about 5 to about 500 .ANG. with a solubility parameter .delta., such that the absolute value (.delta.-10) [cals/cm.sup.3 ].sup.1/2 is greater than 1 and which is different from the solubility parameter of the solvent and recovered light oil.
U.S. Pat. No. 4,797,200 is directed to upgrading heavy oils by solvent dissolution and ultrafiltration. The process removes metals such as nickel and vanadium from the oil as well as lowering the Conradson Carbon Residue of the resulting oil. In the process, the oil feed is diluted with a solvent which completely solvates the oil and the resulting solution is subjected to ultrafiltration using membranes. A permeate enriched in aromatic and saturated hydrocarbons is recovered.